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Old 03-12-2021, 06:07   #16
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Re: switching from diesel to electric propulsion

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Originally Posted by more View Post
Thermal Energy of 1,5 liter of diesel fuel
Work on your units.

1.5l of diesel can generate anything from a tiny fraction of a KW to many thousands of KW...just depends on how long you expect it to hold that level of power.

15KW is roughly 20HP, it's a bit light for a 38ft monohull but not extremely low. We had a 25hp outboard on our 34ft catamaran and it was quite reasonable allowing us to cruise comfortably at 80% of hull speed and opened up, hull speed was limiting us prior to running out of power.
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Old 03-12-2021, 06:43   #17
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Re: switching from diesel to electric propulsion

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Originally Posted by valhalla360 View Post
Work on your units.

1.5l of diesel can generate anything from a tiny fraction of a KW to many thousands of KW...just depends on how long you expect it to hold that level of power.

15KW is roughly 20HP, it's a bit light for a 38ft monohull but not extremely low. We had a 25hp outboard on our 34ft catamaran and it was quite reasonable allowing us to cruise comfortably at 80% of hull speed and opened up, hull speed was limiting us prior to running out of power.
1 litre of diesel-oil around 10,0 kwh 35,9 mJ
Thermal energy content of 1 liter of petrol = 7800 kcal

Mechanical energy on shaft diesel engine from 1 liter diesel fuel is 3,3 kwh
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Old 03-12-2021, 06:51   #18
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Re: switching from diesel to electric propulsion

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1 litre of diesel-oil around 10,0 kwh 35,9 mJ
Thermal energy content of 1 liter of petrol = 7800 kcal

Mechanical energy on shaft diesel engine from 1 liter diesel fuel is 3,3 kwh
But you were responding to a comment about the OP spec'ing a 15kw motor and it's ability to fight a headwind by comparing it to the power of 1.5l of diesel fuel. 1.5l of diesel does not directly correlate to power without a time factor applied.

If you dump that 1.5l of diesel into a large enough motor at a fast enough rate, it will easily handle the headwind or conversely if you trickle it in slowly enough, you will be blown backwards as it's not generating enough power.

Power and energy are different things.
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Old 03-12-2021, 10:11   #19
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Re: switching from diesel to electric propulsion

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Regarding range: We kept the diesel tank, it's got a capacity of 150l. Using the generator, we will have the same or even better range than before.
Sorry, I overlooked the generator in your preceding post. Thank you for the reply.
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Old 04-12-2021, 04:16   #20
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Re: switching from diesel to electric propulsion

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Originally Posted by mako View Post
How many kWh do you expect to use at your designed cruise speed of 4-5 knots? Will you genset provide that much power, because the battery bank isn't very large.

The generator will provide a maximum of 10kW. Consequently, max. power consumption while cruising should be below 8kW. In this power range I hope (and expect) to achieve 4-5 kts.


As quoted before, the battery capacity is 4 x 7.2 kWh = 28.8 kWh. This should do.



Thanks for your comment.
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Old 04-12-2021, 04:19   #21
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Re: switching from diesel to electric propulsion

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That's a lot more reasonable then.

Still please share the test results.

Thank you. Of course, I will share the results of the first test runs. Alas, this won't happen before March or rather April.
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Old 04-12-2021, 04:26   #22
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Re: switching from diesel to electric propulsion

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15kW seems very small. Is that going to be enough? Say you are going up Lefkas canal with a stiff headwind?

Of course, we will have less power compared to what we had with the Volvo D2-55F. However, I do expect the 15kW setup to be sufficient. The first test runs will show whether we were right or not.



Lefkas canal is just around the corner, so I will definitely take the boat there. ;-)
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Old 04-12-2021, 04:50   #23
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Re: switching from diesel to electric propulsion

@Xiam, I like your setup. Enough battery power for getting in and out of the harbor (say 1 hour total) then a genset as “get home” power at 4 knots. This is how trawlers do it also.

However do remember that to keep that 10kW genny healthy you’ll need to run it weekly for a couple of hours at minimum 30% (50% is better) load. Which means draining that lithium bank down to 80% DOD so you can put it back in heavily.

I hope it works out well for you.
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